How giant sea creatures eat tiny sea creatures - Kelly Benoit-Bird

Transcriber: Andrea McDonough Reviewer: Jessica Ruby

One of the reasons that I'm fascinated by the ocean

is that it's really an alien world on our own planet.

From our perspective,

sitting on the shoreline or even out on a boat,

we're given only the tiniest glimpses

at the real action that's happening

beneath the surface of the waves.

And even if you were able to go down there,

you wouldn't see very much

because light doesn't travel very far in the ocean.

So, to answer questions about how the ocean works,

in my research, we use sound.

We use sonars that send out pulses of sound

made up of a number of different frequencies, or pitches,

that are shown with different colors.

That sound bounces off things in the habitat

and comes back to us.

If it were to bounce off this dolphin,

the signal we got back

would look very much like the one we sent out

where all the colors are represented pretty evenly.

However, if we were to bounce

that same sound off of a squid,

which in this case is about the same size as that dolphin,

we'd instead only get the lowest frequencies back strongly,

shown here in the red.

And if we were to look at the prey of that squid,

the tiny little krill that they're eating,

we would instead only get the highest frequencies back.

And so by looking at this,

we can tell what kinds of animals are in the ocean,

we can look at how dense they are,

where they are distributed,

look at their interactions

and even their behavior

to start to study the ecology of the ocean.

When we do that, we come up with

something sort of surprising:

on average, there isn't very much food in the ocean.

So even in places which we think of as rich, the coasts,

we're talking about two parts of every million contain food.

So what does that mean?

Well, that means that in the volume of this theater,

there would be one tub of movie theater popcorn

available to be eaten.

But of course, it wouldn't be collected

for you neatly in this bucket.

Instead, you'd actually have to be swimming

through this entire volume Willy Wonka style,

picking off individual kernels of popcorn,

or perhaps if you were lucky,

getting a hold of a few small clumps.

But, of course, if you were in the ocean,

this popcorn wouldn't be sitting here

waiting for you to eat it.

It would, instead, be trying to avoid becoming your dinner.

So I want to know how do animals solve this challenge?

We're going to talk about animals in the Bering Sea.

This is where you may have see "Deadliest Catch" framed,

in the northernmost part of the Pacific Ocean.

We've been looking specifically at krill,

one of the most important food items in this habitat.

These half-inch long shrimp-like critters

are about the caloric equivalent

of a heavily buttered kernel of popcorn.

And they're eaten by everything

from birds and fur seals that pick them up one at a time

to large whales that engulf them in huge mouthfuls.

So I'm going to focus in the area

around three breeding colonies for birds and fur seals

in the southeastern Bering Sea.

And this is a map of that habitat

that we made making maps of food

the way we've always made maps of food.

This is how many krill are in this area of the ocean.

Red areas represent lots of krill

and purple basically none.

And you can see that around the northern two most islands,

which are highlighted with white circles

because they are so tiny,

it looks like there's a lot of food to be eaten.

And yet, the fur seals and birds on these islands

are crashing.

Their populations are declining

despite decades of protection.

And while on that southern island

at the very bottom of the screen

it doesn't look like there's anything to eat,

those populations are doing incredibly well.

So this left us with a dilemma.

Our observations of food don't make any sense

in the context of our observations of these animals.

So we started to think about how we could do this differently.

And this map shows not how many krill there are,

but how many clumps of krill there are,

how aggregated are they.

And what you get is a very different picture of the landscape.

Now that southern island looks

like a pretty good place to be,

and when we combine this

with other information about prey,

it starts to explain the population observations.

But we can also ask that question differently.

We can have the animals tell us what's important.

By tagging and tracking these animals

and looking at how they use this habitat,

we are able to say, "What matters to you?"

about the prey.

And what they've told us

is that how many krill there are really isn't important.

It is how closely spaced those krill are

because that's how they are able to make a living.

We see the same pattern

when we look in very different ocean,

further south in the Pacific,

in the warm waters around the Hawaiian islands.

So a very different habitat,

and yet the same story.

Under some conditions,

the physics and the nutrients, the fertilizer,

set up aggregations in the plants, the phytoplankton.

And when that happens,

these very dense aggregations of phytoplankton

attract their predators,

which themselves form very dense layers.

That changes the behavior and distribution

of their predators as well,

starting to set up how this entire ecosystem functions.

Finally, the predators that eat

these small fish, shrimp, and squid,

we're talking about two- to three-inch long prey here,

changes how they use their habitat

and how they forage.

And so we see changes in the spinner dolphins

that are related to the changes

we're seeing in the plant life.

And just by measuring the plants,

we can actually predict very well

what's going to happen in the top predator

three steps away in the food web.

But what's interesting is

that even the densest aggregations of their prey

aren't enough for spinner dolphins to make it.

It's a pretty tough life there in the ocean.

So these animals actually work together

to herd their prey into even denser aggregations,

starting with patches that they find in the first place.

And that's what you're going to see in this visualization.

We have a group of 20 dolphins,

you notice they're all set up in pairs,

that are working together

to basically bulldoze prey

to accumulate it on top of itself.

And once they do that,

they form a circle around that prey

to maintain that really dense patch

that is a couple thousand times higher density

than the background that they started with

before individual pairs of dolphins

start to take turns feeding

inside this circle of prey that they've created.

And so, this work is showing us

that animals can first give us the answers

that aggregation is critical to how they make their living.

And by looking more deeply at the ocean,

we're starting to understand our interactions with it

and finding more effective ways of conserving it.

Thank you.